A precision figure is meaningful only when the repeated work is defined. Reinjecting one peptide solution tests a narrower part of the procedure than preparing fresh standards and samples on several days. Both can be useful, but they answer different questions about how the assay behaves.
Define the conditions behind each precision term
The JCGM vocabulary describes repeatability conditions through the same procedure, operators, measuring system, location and operating conditions over a short period. The exact set of fixed conditions should be stated.JCGM VIM — Repeatability conditions (opens in a new tab)
Intermediate precision keeps the procedure and location while allowing specified changes over a longer period, such as operators or measuring systems. The term does not mean that every possible source of routine variation was necessarily studied.JCGM VIM — Intermediate precision conditions (opens in a new tab)
| Repeated work | Variation represented |
|---|---|
| Several injections from one solution | The injection and measurement stage under those conditions |
| Independent preparations in one run | Preparation plus the included measurement stages |
| Preparations across defined days or operators | The included within-laboratory changes |
“Tested six times” is therefore incomplete. Six readings from one prepared vial and six independently prepared portions cannot be treated as the same design.
Look for differences between groups as well as within them
For an original example, day one gives 9.99, 10.00 and 10.01 mg, while day two gives 10.29, 10.30 and 10.31 mg. Each day has a sample standard deviation of 0.01 mg, but the daily means differ by 0.30 mg.
The small within-day spread does not describe the difference between days. If the results are intended for routine use across days, the broader variation must be considered rather than quoting only the tighter figure.
A pooled calculation can summarise variability, but it does not by itself explain its source. Preserve the group labels and the design before reducing the data to a single RSD.
Include the stages that matter for the reported result
Walsh and colleagues used a nested experimental design to investigate preparation of analytical standards for a lyophilised peptide substance. They found important variation associated with preparation factors, including sonication, balance and preparation scale.Walsh and colleagues — Sources of variance in peptide analytical-standard preparation (opens in a new tab)
The study demonstrates why a stable chromatographic measurement can coexist with a more variable preparation process. It does not establish the dominant source of variation in another peptide assay.
A common standard solution shared by every replicate can hide variability in standard preparation. A common extraction shared by every injection can similarly leave extraction variation unmeasured.
Identify the point at which replicates became independent. That point determines which earlier stages are held constant and which later stages can contribute to the observed spread.
If the intended report is an average of several measurements, evaluate that reporting procedure explicitly. Precision of an individual result and precision of an average are related but different quantities.
Make the precision figure reusable by another reader
A useful summary includes the concentration or material level, number of independent preparations, injections per preparation, changed conditions and statistical measure. “RSD 1%” without those details cannot show what variability the figure covers.
Broader conditions may produce a larger spread than a tightly controlled repeatability experiment. That is not automatically evidence of an error; it can reflect the additional variation the broader study was designed to include.
Precision also remains separate from agreement with an external reference. A consistent calibration bias can persist across operators and days, so intermediate precision does not alone demonstrate accurate content assignment.
Sources and further detail
- JCGM VIM — Repeatability conditions (opens in a new tab)
Official definition of the fixed-condition, short-period measurement setting.
- JCGM VIM — Intermediate precision conditions (opens in a new tab)
Official definition of within-location precision with specified changes.
- Walsh and colleagues — Sources of variance in peptide analytical-standard preparation (opens in a new tab)
AAPS PharmSciTech 21, 70 (2020), DOI 10.1208/s12249-020-1623-5. Primary nested-ANOVA study; preparation findings are material-specific.
Sources checked 19 September 2026. Worked examples are illustrative unless a supplied report is explicitly identified. This article has not undergone independent scientific peer review.